Presently, the paint delivery systems which are utilized for the finishing of a wide variety of manufactured items such as motor vehicles, household appliances and the like are becoming increasingly more sophisticated. A typical industrial paint delivery system may comprise a central paint supply having a number of painting stations communicating therewith. Such paint delivery systems can selectably deliver a variety of different paints to a given painting station and include complex fluid pathways involving various tanks, pumps and conduits. These paint delivery systems tend to become clogged with encrustations in the course of their use and such deposits can decrease and even block the flow of paint therethrough. Such clogging is occasioned by deposits of pigment, resins or other components of the paint within the tanks and lines of the system. In addition to causing clogging, such deposits can also contaminate the paint color, and can cause surface defects in the finished, painted product. Cleaning the paint delivery system reduces the amount of surface repairs to paint finishes.
The build-up of residues necessitates periodic cleaning of paint delivery systems and because of the complexity of the systems and the necessity of avoiding expensive downtime, it is generally preferable that such systems be cleaned without disassembly. The prior art approach to cleaning involves passing a variety of solvents, detergents or other cleaners through the system, and tends to involve numerous steps and multiple compositions. It should be noted that these processes often do not provide full removal of deposits, particularly pigment residues.
A typical prior art process can involve flushing five or more different cleaning compounds of varying polarity through the paint system and can include 30 separate operational steps. The numerous cleaning compounds are needed in order to fully remove the residues in the system and to ensure compatibility of any cleaner residue remaining in the system with subsequently introduced paint. As a result, the system must be sequentially rinsed with various materials in a predetermined order such that the final rinse is with a paint-compatible thinner. Clearly, it would be most advantageous to reduce the number of steps by utilizing a cleaning composition which is, fully paint-compatible and to improve the efficiency of the process by utilizing a composition capable of removing all residues.
Many prior art cleaning compositions also present problems of waste disposal. The cleaning compositions may be broadly categorized as either organic based or aqueous based. The organic based materials can employ halogenated and/or aromatic solvents as well as reagents such as acetone, methyl ethyl ketone, and the like. These solvents are toxic, and in many instances flammable and present problems cf disposal as well as compatibility with the components of the pain: delivery system. The aqueous solvents generally comprise highly caustic materials such as potassium hydroxide or sodium hydroxide or acidic materials such as acetic acid, all of which present dangers in both handling and disposal. Many of the aforementioned solvents, particularly the aqueous based ones, are not compatible with subsequently utilized paint and hence elaborate rinse procedures are needed before the cleaned equipment may be put back into service. In addition to the foregoing shortcomings, prior art paint system cleaning solvents do not provide sufficient cleaning action, particularly with regard to encrusted pigment deposits and, as a consequence, long flush times and/or repeated cleaning cycles have been generally required.
It has been known to utilize abrasive materials to clean closed lines and one such process is disclosed in U.S. Pat. No. 4,572,744 which describes the use of sand or similar material entrained in a flow of air to clean the interior of boiler tubes. Also mentioned in the '744 patent is the similar use of liquid based abrasive slurries to clean pipes.
Heretofore, various attempts have been made to utilize abrasive based materials for cleaning paint lines and it is known to employ mica, or sand particles in conjunction with a flush liquid to scour the interior of paint lines. Problems have arisen with the use of such inorganic abrasives insofar as they can be relatively hard and tend to damage or clog pumps and passageways through which they flow. Additionally, such inorganic abrasive materials are also relatively dense and tend to settle out of a cleaning fluid unless vigorous agitation is maintained or thickeners are added to increase the solution viscosity.
It is known to utilize a specific paint system cleaning composition comprised of sand or mica suspended in a solution of xylene and methyl isobutyl ketone thickened with a resinous material. Compositions of this type present problems insofar as the resin and abrasive are difficult to rinse from the system thereby presenting problems of contamination, particularly when the resin is not compatible with subsequently employed paint compositions; additionally, the viscous composition presents problems of waste disposal insofar as the resin is difficult to incinerate and inhibits the ready evaporation and recovery of the xylene and ketone. Obviously, the inorganic abrasive residue presents significant waste disposal problems insofar as it cannot be readily incinerated.
The present invention overcomes various shortcomings of prior art cleaning compositions and methods insofar as it provides a group of simple to use compositions which are readily compatible with a variety of paint formulations and which can be readily incinerated or recycled.
The cleaning compositions of the present invention include a particulate organic abrasive material. Organic, polymeric materials are not generally thought of as being abrasive; however the present invention relies in part upon the counter intuitive finding that organic materials can function very well to facilitate the cleaning of encrustations from paint delivery systems. The polymeric particles utilized in this invention are of relatively low density and hence may be maintained in suspension without resort to thickeners or vigorous agitation. Although these organic materials perform an excellent job of cleaning residues from paint lines, they are not sufficiently abrasive to damage pumps, valves and the like. The compositions of the present invention may be advantageously utilized in cleaning the lines and tanks of paint delivery systems as well as for other cleaning purposes where some degree of abrasive action is required. The relatively low viscosity of the cleaning compositions of the present invention simplifies their disposal or recycling and the fact that they contain no inorganic solids allows for their ready incineration. These and other advantages of the present invention will be readily apparent from the drawings, discussion, description and claims which follow.